{ "schemaVersion": 1, "attribution": [ { "source": "CISA Known Exploited Vulnerabilities", "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog", "licence": "US government work" }, { "source": "GitHub Advisory Database", "url": "https://github.com/advisories", "licence": "CC BY 4.0" }, { "source": "Have I Been Pwned", "url": "https://haveibeenpwned.com/", "licence": "CC BY 4.0" }, { "source": "CVE Program (CVE records)", "url": "https://www.cve.org/Legal/TermsOfUse", "licence": "CVE Terms of Use", "notice": "Copyright © 1999-2026, The MITRE Corporation. CVE is a trademark and the CVE logo is a registered trademark of The MITRE Corporation.", "terms": "CVE Usage: MITRE hereby grants you a perpetual, worldwide, non-exclusive, no-charge, royalty-free, irrevocable copyright license to reproduce, prepare derivative works of, publicly display, publicly perform, sublicense, and distribute Common Vulnerabilities and Exposures (CVE™). Any copy you make for such purposes is authorized provided that you reproduce MITRE's copyright designation and this license in any such copy." }, { "source": "FIRST EPSS", "url": "https://www.first.org/epss/", "licence": "free to use; FIRST requests attribution" } ], "record": { "id": "CVE-2021-47465", "sourceURL": "https://www.cve.org/CVERecord?id=CVE-2021-47465", "idYear": 2021, "status": "PUBLISHED", "publishedAt": "2024-05-22T06:23:25.027Z", "updatedAt": "2026-08-05T08:47:58.408Z", "importedAt": "2026-10-24T01:56:36.661Z", "snapshot": { "id": "cve_2026-10-24_midnight_baseline", "at": "2026-10-24T00:00:00.000Z", "source": "https://github.com/CVEProject/cvelistV5/releases/tag/cve_2026-10-24_0100Z" }, "facts": { "title": "KVM: PPC: Book3S HV: Fix stack handling in idle_kvm_start_guest()", "summary": "In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: PPC: Book3S HV: Fix stack handling in idle_kvm_start_guest()\n\nIn commit 10d91611f426 (\"powerpc/64s: Reimplement book3s idle code in\nC\") kvm_start_guest() became idle_kvm_start_guest(). The old code\nallocated a stack frame on the emergency stack, but didn't use the\nframe to store anything, and also didn't store anything in its caller's\nframe.\n\nidle_kvm_start_guest() on the other hand is written more like a normal C\nfunction, it creates a frame on entry, and also stores CR/LR into its\ncallers frame (per the ABI). The problem is that there is no caller\nframe on the emergency stack.\n\nThe emergency stack for a given CPU is allocated with:\n\n paca_ptrs[i]->emergency_sp = alloc_stack(limit, i) + THREAD_SIZE;\n\nSo emergency_sp actually points to the first address above the emergency\nstack allocation for a given CPU, we must not store above it without\nfirst decrementing it to create a frame. This is different to the\nregular kernel stack, paca->kstack, which is initialised to point at an\ninitial frame that is ready to use.\n\nidle_kvm_start_guest() stores the backchain, CR and LR all of which\nwrite outside the allocation for the emergency stack. It then creates a\nstack frame and saves the non-volatile registers. Unfortunately the\nframe it creates is not large enough to fit the non-volatiles, and so\nthe saving of the non-volatile registers also writes outside the\nemergency stack allocation.\n\nThe end result is that we corrupt whatever is at 0-24 bytes, and 112-248\nbytes above the emergency stack allocation.\n\nIn practice this has gone unnoticed because the memory immediately above\nthe emergency stack happens to be used for other stack allocations,\neither another CPUs mc_emergency_sp or an IRQ stack. See the order of\ncalls to irqstack_early_init() and emergency_stack_init().\n\nThe low addresses of another stack are the top of that stack, and so are\nonly used if that stack is under extreme pressue, which essentially\nnever happens in practice - and if it did there's a high likelyhood we'd\ncrash due to that stack overflowing.\n\nStill, we shouldn't be corrupting someone else's stack, and it is purely\nluck that we aren't corrupting something else.\n\nTo fix it we save CR/LR into the caller's frame using the existing r1 on\nentry, we then create a SWITCH_FRAME_SIZE frame (which has space for\npt_regs) on the emergency stack with the backchain pointing to the\nexisting stack, and then finally we switch to the new frame on the\nemergency stack.", "affected": [ { "vendor": "Linux", "product": "Linux", "defaultStatus": "unaffected", "versions": [ { "version": "10d91611f426d4bafd2a83d966c36da811b2f7ad", "status": "affected", "versionType": "git", "lessThan": "80bbb0bc3a0288442f7fe6fc514f4ee1cb06ccb7" }, { "version": "10d91611f426d4bafd2a83d966c36da811b2f7ad", "status": "affected", "versionType": "git", "lessThan": "fbd724c49bead048ae9fc1a5b7bff2fb3e54f855" }, { "version": "10d91611f426d4bafd2a83d966c36da811b2f7ad", "status": "affected", "versionType": "git", "lessThan": "6d077c37c4643394b1bae9682da48164fc147ea8" }, { "version": "10d91611f426d4bafd2a83d966c36da811b2f7ad", "status": "affected", "versionType": "git", "lessThan": "9b4416c5095c20e110c82ae602c254099b83b72f" } ] }, { "vendor": "Linux", "product": "Linux", "defaultStatus": "affected", "versions": [ { "version": "5.2", "status": "affected" }, { "version": "0", "status": "unaffected", "versionType": "semver", "lessThan": "5.2" }, { "version": "5.4.156", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "5.4.*" }, { "version": "5.10.76", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "5.10.*" }, { "version": "5.14.15", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "5.14.*" }, { "version": "5.15", "status": "unaffected", "versionType": "original_commit_for_fix", "lessThanOrEqual": "*" } ] } ] } } }